Increased building costs and improvements in the ability to construct effective roof trusses have resulted in an increasing use of prefabricated roof trusses in the construction of both commercial and residential buildings. Roof trusses, which are assembled at a manufacturing facility, are moved to the job site most commonly on a tractor-trailer operated on the highway system. Because of the differing requirements of the buildings, the dimensions and configurations of the trusses vary markedly from building to building. As a result, the trailers utilized to transport the trusses must be capable of adaptation in order to handle the various sizes and configurations of trusses which may be fabricated in a single manufacturing plant.
Conventional tractor-trailer combinations for moving trusses consist of a standard over-the-road tractor equipped with a "fifth wheel" coupler by which a trailer may be connected to the tractor. A first bolster is mounted above the trailer portion of the "fifth wheel" coupler to support the front end of the trusses. An independent rear trailer is equipped with a similar bolster to support the rear end of the trusses. The independent trailer/bolster assembly is connected to the "fifth wheel" coupling mechanism through a pipe structure. The distance between the front bolster and the rear bolster may be adjusted by moving the trailer along a cylindrical pipe which serves as the backbone of the truck. In cases where the trusses have a high pitch or are very long, a vertical extension may be added to the front and rear bolsters to increase the height thereof so that longer or deeper trusses may be carried on the tractor-trailer without the apex of the truss dragging on the ground.
Adapting the trailers for various sizes of trusses is quite labor intensive. Adjusting the distance between the front and rear bolsters usually requires two people; one person to drive the tractor and one person to signal the driver when locking holes are lined up in the pipe structure. Several men are required to carry the vertical extension bolsters and mount them on the truck when increased height is needed. If the tractor breaks down, it becomes necessary to unload the trusses before the tractor can be moved away from the trailer and a new tractor connected. This process as well requires numerous men to effect.
Another problem with conventional tractor-trailer combinations is the inability to adjust the height of the load after the trusses are mounted. This can create an extreme safety hazard. In one known instance, a tractor-trailer carrying trusses attempted to cross a railroad grade crossing. The clearance was such that the trusses grounded on the center of the grade and effectively "hung up" the tractor-trailer combination. Before the tractor-trailer could be moved from the railroad crossing, it was necessary to get additional equipment to unload the trusses. Obviously if a train had arrived in the meantime, the results could have been disastrous.
Accordingly one object of the instant invention is to provide a trailer which is capable of standing alone in a loaded condition. A further object of the invention is to provide a trailer which may be adjusted in length by one man. Yet another object of the instant invention is to provide a trailer which can be adjusted in height in either the loaded or unloaded condition. Still another object of the invention is to provide a trailer which is stable in instances where the load on one side of the trailer exceeds the load on the opposite side of the trailer. These and other objects and advantages of the present invention will be in part apparent and in part pointed out hereinafter.